Printing by an ink jet method has rapidly spread and used for various purposes because printing of the same image quality as in the conventional multi-color printing or color photographic system is feasible, speeding up or multi-coloring is easily made, and the cost is lower than the conventional printing methods in case of a small number of sheets to be printed.
In the printing by the ink jet method, a recording sheet having on a substrate sheet an ink-receptive layer formed by coating the substrate sheet with a water-soluble polymer such as polyvinyl alcohol is employed, and on the sheet, printing is carried out by the use of a water base ink. The resulting print, however, has insufficient water resistance, and there is a problem of lowering of image quality in the case where the print is placed in environment of high moisture or is wetted by water. Further, there is another problem that an image of high sharpness and high precision cannot be obtained because the recording sheet used has insufficient ink absorption characteristics.
To solve such problems, a recording sheet wherein an ink-receptive layer containing fine particles of silica, alumina or the like is formed on a substrate sheet is proposed.
For example, in Japanese Patent Laid-Open Publication No. 149475/1987, a recording sheet wherein an ink-receptive layer containing spherical particles of silica or the like having an average particle diameter of 1 to 50 μm is formed is described. In Japanese Patent Publication No. 24906/1991, a recording medium having an ink-receptive layer containing cationic hydrated aluminum oxide is described. In Japanese Patent Publication No. 19037/1992, a recording medium having a receptive layer containing cationic colloidal silica is described. In Japanese Patent Laid-Open Publication No. 115984/1992, a recording sheet wherein a layer of pseudo-boehmite alumina is formed on a substrate and a layer of porous silica is further provided thereon is described. In Japanese Patent Laid-Open Publication No. 55829/1994, a recording sheet having on a substrate a layer of porous silica particles having an average particle diameter of 2 to 50 μm, an average pore diameter of 8 to 50 nm and a pore volume of 0.8 to 2.5 cc/g and further having thereon a pseudo-boehmite porous layer obtained by drying an alumina sol is described.
Most of these recording sheets are intended for printing using dye type inks, but because the dye type inks have poor weathering resistance, the resulting prints have disadvantages such as discoloration or decoloring caused by exposure to ultraviolet light, oxygen, ozone or the like, and such disadvantages are markedly observed especially when the prints are used outdoors.
Therefore, pigment type inks having excellent weathering resistance came to be used even in the ink jet printing method.
Pigment particles, however, are particles usually having diameters of 10 to 500 nm, and the conventional ink-receptive layer does not have pores capable of effectively absorbing such large particles, so that there resides problems such that the pigment particles remain on the ink-receptive layer surface without being absorbed by the ink-receptive layer, the ink-receptive layer exhibits insufficient water resistance, and the pigment particles are removed by rubbing to cause crocking.
The present invention is intended to solve such problems associated with the prior art as described above, and it is an object of the invention to provide a recording sheet with an ink-receptive layer which can be used not only for dye type inks but also for pigment type inks, has excellent printing properties such that a print free from ink blotting is obtainable and clear printing with uniform density is feasible, is excellent in water resistance, weathering resistance and fading resistance and has sufficiently high strength, and a coating liquid for forming an ink-receptive layer.
In particular, it is an object of the invention to provide a recording sheet with an ink-receptive layer which is desirable for high-speed printing by an ink jet method and is favorably used also as a recording sheet, such as white color PET for large size color printer or art paper, or a recording sheet having no absorption characteristics and needing transparency, and a coating liquid for forming an ink-receptive layer.